This invention relates generally to helmets, and more particularly to helmet structures worn by cyclists and consisting of different density materials, as for example foamed synthetic resin.
Safety helmets, as worn by bicyclists, motorcyclists, skaters, and others, typically employ a thick (20 to 50 mm) layer of crushable, synthetic resin foam, extending over and about the wearer's head to mitigate impact. In many designs, ventilation openings or holes are formed to extend in or through the helmet body. It was found that such holes reduced the impact strength of the helmet body, and particularly proximate the holes. In order to prevent reduction in impact strength, a stiff, outer shell was employed, the helmet body itself would be made thicker, or the entirety of the crushable foam would be made of higher density material. However, all of these approaches increase substantially the overall weight of the helmet. No way was known to achieve increased strength, without increasing helmet body thickness or weight.